Flat plate wall surface fluid frictional resistance measuring system and method based on elastic deformation body

Abstract

A flat plate wall fluid frictional resistance measuring system and method based on an elastic deformation body comprises a circulating water tunnel platform and a resistance measuring unit, the circulating water tunnel platform is used for providing liquid flowing environments with different flow speeds, the resistance measuring unit comprises the elastic deformation body, and the upper surface of the elastic deformation body is pasted on a cover plate. The cover plate is connected to the experiment section flow channel reserved window through a clamp; a transition block is arranged in front of the incident flow direction of the elastic deformable body and is connected with the experimental section flow channel; the transition block is adhered to the cover plate; a 45-degree strain gauge is adhered to the side surface of the elastic deformation body and is connected with the signal processing system; a to-be-tested flat plate sample is adhered to the bottom surface of the elastic deformation body; according to the invention, through deformation of an elastic material, tangential force measurement is converted into easily-measured dependent variable for measurement, the elastic material with low shear modulus and easy deformation is used to deform and amplify a tiny tangential force material, and through a strain sensor and a signal processing system, the material deformation is converted into a voltage signal and amplified, so that accurate measurement is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of flat plate wall friction resistance measurement, and in particular to a flat plate wall fluid friction resistance measurement system and method based on an elastic deformable body. Background Art

[0002] Measuring fluid friction is crucial for characterizing drag reduction performance. Researchers have extensively studied techniques for measuring flat wall friction. Flat wall friction originates from the surface normal velocity gradient, which is parallel to the wall and is a tangential force. This tangential force is difficult to measure directly and must be converted into other readily measurable physical quantities, such as tension, pressure, displacement, and deformation.

[0003] Currently, there are three main types of commonly used measurement systems for the friction resistance of flat plate walls: particle image velocimetry (PIV) system, pressure differential system, and balance system; the particle image velocimetry (PIV) system is expensive, the data results are not intuitive, and the data processing and calculation amount is large; the pressure differential system is easily affected by flow field fluctuations, has large errors, and insufficient measurement accuracy; the balance system (such as CN110823499A, CN108955956A, CN101832852A, CN1793810A, etc.) converts friction resistance into positive pressure through mechanical devices, has a complex structure, and due to factors such as friction between mechanical devices, the measurement results include other forces in addition to the friction resistance of the flat plate wall. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a flat wall fluid friction resistance measurement system and method based on an elastic deformable body. The tangential force measurement is converted into an easily measurable strain through the deformation of the elastic material. A low shear modulus and easily deformable elastic material is used to deform and amplify the tiny tangential force material. Through a strain sensor and a signal processing system, the material deformation is converted into a voltage signal, and the signal is further amplified, thereby realizing accurate measurement of tiny resistance changes.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A flat-plate wall fluid friction resistance measurement system based on an elastic deformable body includes a circulating water tunnel platform and a resistance measurement unit. The circulating water tunnel platform is used to provide a liquid flow environment with different flow rates. The resistance measurement unit includes an elastic deformable body 11, which is pasted on a cover plate 15. The cover plate 15 is connected to a reserved window of an experimental section flow channel 16 through a clamp 17; a transition block 14 is provided in front of the elastic deformable body 11 in the flow direction and connected to the experimental section flow channel 16, and the transition block 14 is pasted on the cover plate 15; a 45° strain gauge 12 is pasted on the side of the elastic deformable body 11, and the 45° strain gauge 12 is connected to a signal processing system; and a flat plate sample 13 to be measured is pasted on the bottom surface of the elastic deformable body 11.

[0007] The elastic deformable body 11 is a regular flat cuboid; it is made of materials such as silicone, rubber, thermoplastic elastomer TPE, etc. that can produce elastic deformation, have a shear modulus of no more than 5 MPa, and a measurable shear modulus.

[0008] When the flat plate sample 13 to be tested is subjected to surface friction resistance of the surface fluid, a shear stress along the flow direction is generated on the lower surface of the elastic deformable body 11, causing the elastic deformable body 11 to deform. The 45° strain gauge 12 deforms along with the elastic deformable body 11, and the strain amount of the elastic deformable body 11 in the 45° direction is detected. The strain amount of the 45° strain gauge 12 is converted into a voltage signal through the signal processing system, and the strain magnitude is calculated based on the voltage signal. The flow direction shear stress magnitude is calculated based on the shear modulus of the elastic deformable body 11 and the relevant knowledge of material mechanics.

[0009] A measurement method using a flat plate wall fluid friction resistance measurement system based on an elastic deformable body includes the following steps:

[0010] S1. Cut the flat sample 13 to be tested and align and stick it to the elastic deformable body 11;

[0011] S2. Process the transition block 14 and stick it on the cover plate 15 so that the front end of the transition block 14 is flush with the wall of the experimental section flow channel 16 and the rear end is flush with the surface of the flat sample 13 to be tested, and the transition from the front end to the rear end of the transition block 14 is smooth;

[0012] S3. Place the cover plate 15 on the reserved window of the experimental section flow channel 16 and fix it with the clamp 17;

[0013] S4, setting the output voltage of the signal processing system to zero;

[0014] S5. Start the axial flow pump 5 of the circulating water tunnel platform and read the flow rate of the ultrasonic flowmeter 7. After the flow rate stabilizes, read the strain value ε of the 12-line strain gauge at 45°. -45° Converted into voltage signal U;

[0015] S6. The linear strain of the elastic deformable body 11 in the 45° direction is calculated based on the voltage signal as ε-45° According to the knowledge of material mechanics, the strain angle γ of the elastic deformable body 11 is calculated as 2ε. -45° The magnitude of the flow direction shear stress on the elastic deformable body 11 is τ=G·γ. The area of ​​the flat plate sample 13 to be tested in the flow field is measured to be S, and the total friction resistance it is subjected to is F=τ·S.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The measurement system and method of the present invention use an elastic deformable body to convert wall shear force into material deformation for measurement. It has no mechanical force transmission device, does not require sophisticated instruments, and has a simple structure. The use of materials with low shear modulus can produce greater deformation under smaller friction resistance, has an amplifying effect on small resistance, and has high measurement accuracy. Only the deformation caused by flow direction shear force is detected, and the disturbance perpendicular to the flow direction is filtered out. Based on the conversion relationship between the detected physical quantities, the friction resistance can be directly obtained, and the data results are intuitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the overall structure of the measurement system of the present invention.

[0019] Figure 2 It is a structural schematic diagram of the test section resistance measurement unit in the measurement system of the present invention.

[0020] Figure 3 This is a schematic diagram of the test principle of the test section resistance force measuring unit structure in the measurement system of the present invention.

[0021] Figure 4 This is a flow chart of the measurement method of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below with reference to embodiments and accompanying drawings.

[0023] Reference Figure 1 , a flat-plate wall fluid friction resistance measurement system based on elastic deformable body, including a circulating water tunnel platform and a resistance measurement unit; the circulating water tunnel platform is connected by a first diameter-reducing section 8, an experimental section 1, a rectifying section 2, a diversion section 3, a butterfly valve 4, an axial flow pump 5, a water tank 6, an ultrasonic flowmeter 7, and a second diameter-reducing section 9, and the circulating water tunnel platform is used to provide a liquid flow environment with different flow rates; refer to Figure 2The resistance measurement unit set in the experimental section 1 includes an elastic deformable body 11, a 45° strain gauge 12, a flat sample 13 to be measured, a transition block 14, a cover plate 15, an experimental section flow channel 16, and a clamp 17; the elastic deformable body 11 is pasted on the cover plate 15, and the cover plate 15 is connected to the reserved window of the experimental section flow channel 16 through the clamp 17; a transition block 14 is provided in front of the elastic deformable body 11 in the flow direction and connected to the experimental section flow channel 16, and the transition block 14 is pasted on the cover plate 15. The transition block 14 is used to avoid flow field turbulence caused by sudden changes in the cross-sectional area of ​​the flow channel; a 45° strain gauge 12 is pasted on the side of the elastic deformable body 11, and the 45° strain gauge 12 is connected to the signal processing system; the flat sample 13 to be measured is pasted on the bottom surface of the elastic deformable body 11.

[0024] like Figure 1 As shown, the fluid medium is stored in the water tank 6 and is driven by the axial flow pump 5. A part of it flows through the main channel and passes through the second reducing section 9, the rectifying section 2, the experimental section 1, and the first reducing section 8 in sequence before flowing back to the water tank 6; the other part is diverted through the diversion section 3 and flows directly back to the water tank 6; the experimental section 1 is a flow channel made of acrylic material with a rectangular cross section, and the rectifying section 2 is equipped with a stainless steel grid plate to ensure smooth flow of the internal fluid. The first reducing section 8 and the second reducing section 9 are reducing interfaces made of acrylic material with a rectangular to circular cross section. A butterfly valve 4 is installed on the diversion section 3, which can cooperate with the speed adjustment of the axial flow pump 5 to adjust the fluid flow rate of the experimental section 1 in a wider range and more accurately. The ultrasonic flowmeter 7 measures the flow rate flowing through the experimental section 1. The cross-sectional area of ​​the experimental section 1 is known, and the flow rate of the experimental section is calculated.

[0025] The elastic deformable body 11 is a regular flat cuboid, and is made of silicone, rubber, thermoplastic elastomer TPE or other materials that can produce elastic deformation, have a shear modulus not greater than 5 MPa and a measurable shear modulus.

[0026] In this embodiment, the elastic deformable body 11 has a size of 1000×700×10 mm. Before being pasted on the cover plate 15 for use, the shear modulus of the material used needs to be calibrated. The shear modulus of the material used is calibrated to G according to the material mechanics shear modulus electrical measurement method.

[0027] like Figure 2 、 Figure 3 、 Figure 4 As shown in the figure, when the flat sample 13 to be tested is subjected to the surface friction resistance of the surface fluid, a shear stress along the flow direction is generated on the lower surface of the elastic deformable body 11, causing the elastic deformable body 11 to deform. The 45° strain gauge 12 generates a strain of ε along the -45° direction along with the elastic deformable body 11. -45° The strain of the 45° strain gauge 12 lines is converted into ε by the signal processing system. -45° Converted into a voltage signal U; the signal processing system used in this embodiment is a Wheatstone bridge 1 / 4 bridge circuit, U = k·E·ε-45° / 4, where k is the strain gauge sensitivity coefficient and E is the excitation voltage (V). According to the voltage signal, the linear strain of the elastic deformable body 11 in the 45° direction can be calculated as ε -45° According to the knowledge of material mechanics, the strain angle γ of the elastic deformable body 11 can be calculated as 2ε -45° The magnitude of the flow direction shear stress on the elastic deformable body 11 is τ=G·γ. The area of ​​the flat plate sample 13 to be tested in the flow field is measured to be S, and the total friction resistance it is subjected to is F=τ·S.

[0028] A measurement method using a flat plate wall fluid friction resistance measurement system based on an elastic deformable body includes the following steps:

[0029] S1. Cut the flat sample 13 to be tested into a size of 1000×700 mm and align and stick it to the elastic deformable body 11;

[0030] S2. Process a transition block 14 of appropriate size and stick it on the cover plate 15 so that the front end of the transition block 14 is flush with the wall of the experimental section flow channel 16 and the rear end is flush with the surface of the flat sample 13 to be tested, and the transition from the front end to the rear end of the transition block 14 is smooth;

[0031] S3. Place the cover plate 15 on the reserved window of the experimental section flow channel 16 and fix it with the clamp 17;

[0032] S4, setting the output voltage of the signal processing system to zero;

[0033] S5. Start the axial flow pump 5 and read the flow rate of the ultrasonic flowmeter 7. After the flow rate stabilizes, read the strain value ε of the 12-line strain gauge at 45°. -45° Converted into voltage signal U;

[0034] S6. The linear strain of the elastic deformable body 11 in the 45° direction is calculated based on the voltage signal as ε -45° According to the knowledge of material mechanics, the strain angle γ of the elastic deformable body 11 is calculated as 2ε. -45° The magnitude of the flow direction shear stress on the elastic deformable body 11 is τ=G·γ. The area of ​​the flat plate sample 13 to be tested in the flow field is measured to be S, and the total friction resistance it is subjected to is F=τ·S.

Claims

1. A flat-plate wall fluid friction resistance measurement system based on an elastic deformable body, comprising a circulating water tunnel platform and a resistance measurement unit, wherein the circulating water tunnel platform is used to provide a liquid flow environment with different flow rates, and the resistance measurement unit comprises an elastic deformable body (11), wherein the elastic deformable body (11) is pasted on a cover plate (15), and the cover plate (15) is connected to a reserved window of an experimental section flow channel (16) through a clamp (17); a transition block (14) is provided in front of the elastic deformable body (11) in the flow direction and connected to the experimental section flow channel (16), and the transition block (14) is pasted on the cover plate (15); a 45° strain gauge (12) is pasted on the side of the elastic deformable body (11), and the 45° strain gauge (12) is connected to a signal processing system; and a flat plate sample (13) to be measured is pasted on the bottom surface of the elastic deformable body (11).

2. The system for measuring the frictional resistance of a flat-plate wall fluid based on an elastic deformable body according to claim 1, characterized in that: The elastic deformable body (11) is a regular flat cuboid; it is made of silicone, rubber, thermoplastic elastomer (TPE) which can produce elastic deformation, has a shear modulus not greater than 5 MPa and a measurable shear modulus.

3. The flat-plate wall fluid friction resistance measurement system based on elastic deformable body according to claim 1, characterized in that: When the flat plate sample (13) to be tested is subjected to the surface friction resistance of the surface fluid, a shear stress along the flow direction is generated on the lower surface of the elastic deformable body (11), causing the elastic deformable body (11) to deform. The 45° strain gauge (12) is deformed along with the elastic deformable body (11), and the strain amount of the elastic deformable body (11) in the 45° direction is detected. The strain amount of the 45° strain gauge (12) is converted into a voltage signal through a signal processing system, and the strain amount is calculated according to the voltage signal. The flow direction shear stress amount is calculated based on the shear modulus of the elastic deformable body (11) and the relevant knowledge of material mechanics.

4. A method for measuring the frictional resistance of a flat-plate wall fluid using a system for measuring the frictional resistance of a flat-plate wall fluid based on an elastic deformable body according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, cutting the flat sample (13) to be tested and aligning and pasting it with the elastic deformable body (11); S2, processing the transition block (14), pasting it on the cover plate (15), so that the front end of the transition block (14) is flush with the wall surface of the experimental section flow channel (16), and the rear end is flush with the surface of the flat sample (13) to be tested, and the front end to the rear end of the transition block (14) is smoothly transitioned; S3. Place the cover plate (15) on the reserved window of the experimental section flow channel (16) and fix it with a clamp (17); S4, setting the output voltage of the signal processing system to zero; S5. Start the axial flow pump (5) of the circulating water tunnel platform, read the flow rate of the ultrasonic flow meter (7), and after the flow rate stabilizes, read the linear strain ε of the 45° strain gauge (12). -45° Converted into voltage signal U; S6. According to the voltage signal, the linear strain of the elastic deformable body (11) in the 45° direction is calculated as ε -45° According to the knowledge of material mechanics, the strain angle γ of the elastic deformable body (11) is calculated as 2ε -45° The magnitude of the flow direction shear stress on the elastic deformable body (11) is τ = G·γ. The area of ​​the flat plate sample (13) to be tested in the flow field is measured to be S, and the total friction resistance it is subjected to is F = τ·S.

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